1. Field of the Invention
This invention relates to image processing systems. More particularly it relates to video data preprocessing.
2. Description of the Prior Art
Existing image processing techniques such as optical character recognition (OCR) operate on vertically oriented segments of a scanned image. Flying spot scanners easily yield vertically oriented image data. Newer scanning techniques while less expensive and more reliable because of fewer maintenance problems, include horizontal arrays of scanning devices relatively moveable to the document to be scanned. Scan output image data is stored for later access. The direction in which the relative movement occurs is often perpendicular to image or character orientation, thereby necessitating 90.degree. rotation of stored video access orientation before initiating further steps in the operating cycle.
The prior art suggests accumulation of video data from a plurality of scan lines representing a complete image or an entire character line before performing rotation or other preprocessing functions.
One such method is proposed in the IBM Technical Disclosure Bulletin, Vol. 17, No. 10, March 1975 at page 3026. Disclosed therein is a method and apparatus for, inter alia, transposing a scanned image by serially loading video bits sequentially in a plurality of shift registers each having capacity for a complete scan line. When all registers are loaded the contents of a given cell in each register is sequentially outputted. Access to any cell position is possible only upon completion of the number of shift cycles necessary to bring that cell to the output port of the register. No provision is made for selectively accessing cell locations out of normal sequence.
The disadvantages of shift registers memories when compared to random access memories, lies in the number of cycles required to access a given memory location. Moreover, present day random access memory devices provide fast access times and are cost competitive with shift register memories.
Another prior art rotation scheme taught in a time sharing environment involves serial storage of horizontal video from a complete line of characters in a memory having as many storage words as scan spots. Each word, in turn, has at least as many storage levels as the number of horizontal scans needed to completely cover a line of printed characters. Parallel readout from the memory is carried out in a manner which directs to the recognition logic a bit stream like that which would have been produced by an optical scanner making a series of vertical sweeps through each character in sequence.
The prior art rotation scheme is not readily applicable in a real time environment where access times and delays must be minimized. The described method is dependent on the speed of incoming data and the delay involved in serially storing an entire line of characters could be appreciable.
A further disadvantage of prior art methods is the requirement for costly, large capacity memories for storing the electronic image of the scanned document during various phases of rotation.